A vehicle fuel line system basically includes a fuel tank, a fuel pump and a fuel line that leads from the tank to the vehicle engine to deliver fuel thereto. A fuel regulator is used to maintain the proper amount of pressure in the fuel line and returns excess fuel to the fuel tank. Starting the engine also starts the fuel pump which pumps fuel from the tank and into the fuel line. Pressure builds in the fuel line to maintain the regulated amount of fuel running to the engine. In present day fuel line systems, a check valve that is normally closed is positioned in or near the fuel pump such that when the engine is turned off, the valve closes to maintain the pressure in the fuel line. This is done to prevent a rapid decrease in pressure which would result in boiling of the fuel in the fuel line due to the latent heat of the recently turned off engine. Should the fuel boil, fuel vapors would replace liquid fuel at the fuel injectors resulting in the engine being unable to start until the vapor is purged and replaced by liquid fuel at the injector tips.
While this method has worked well at preventing fuel boiling for this reason, a normally closed valve which remains closed even after engine cooling also undesirably prevents the relief of increasing pressure caused by diurnal heating of the fuel in the fuel lines (e.g., when the vehicle spends a cool night followed by a day without running and sitting in the hot sun). Thus, in a vehicle that has cooled down and then heated back up due to diurnal heating, fuel vapors may form that, due to the high pressure build-up in the fuel line caused by the heat and a normally closed valve, will leak out of the fuel line at seal locations such as the injector tips. While fuel vapor emissions due to diurnal heating have been tolerated in the past, present day federal and state emission regulations prohibit or at least significantly reduce previously accepted emission levels.
There therefore exists a need for a fuel line valve and method that will relieve pressure build-up caused by diurnal heating of a previously cooled engine, and thereby significantly reduce or eliminate fuel vapors from escaping the fuel line due to this phenomenon.